1. Field of the Invention
The present invention relates to a method for driving a liquid crystal display device, and more particularly, to a method for driving multi-layered-type liquid crystal display device comprising stacked plural liquid crystal cells for passing lights of different colors therethrough.
2. Description of Related Art
Liquid crystal display devices are now being used widely used in various electronic apparatuses such as clocks and electronic calculating machines, displays of computer's terminals and word processors, television sets. Recently, there have been extremely high demands for constituting multicolor and full color displays using by liquid crystal display devices. Further, some are already put in practical use in the fields of graphic display and image display. The color display of this type is attained by arranging color filter layers inside of a liquid crystal cell as a light switcher in order to generate various colors. The major display mode of the liquid crystal display device is called a twisted nematic display mode (referred to as a TN display mode hereinafter), wherein liquid crystal molecules are twisted by an angle of 90.degree. in the liquid crystal cell.
However, in the TN display mode, the dependency of the display characteristic on the wavelength of light is relatively large, and it is difficult to switch the light uniformly over the whole range of the visible light. Particularly, in a normally closed type liquid crystal display device in which the polarization axes of two polarizers are parallel to each other, coloring of the display may be caused due to leakage of the light when no voltage is applied to the liquid crystal layer. Therefore, it is difficult to adapt the TN display mode in a full color display.
In a color liquid crystal display device utilizing the TN display mode, wherein the aforementioned color filter layer are arranged, there have been mainly proposed the following two driving methods as methods for driving the color liquid crystal display device. One is an active matrix driving method, and another is a simple multiplex driving method.
In a liquid crystal display device utilizing the active matrix driving method, non-linear devices such as diodes or switching devices such as thin film transistors are provided at respective pixels of the liquid crystal cell, and the liquid crystal layer of each pixel is driven selectively.
In a liquid crystal display device utilizing the simple multiplex driving method, there are not provided nonlinear devices or switching devices, and the liquid crystal layer of each pixel is driven sequentially. In this liquid crystal display device, a steepness near the threshold value gives a trouble among optical characteristics of the liquid crystal, in which the TN display mode is used.
In order to improve the optical characteristics exhibiting the steepness near the threshold value, there has been proposed a Super Twisted Nematic method (referred to as an STN method hereinafter) as a method for orienting liquid crystal molecules, wherein the twisted angle is set so as to have a value between 180.degree. and 270.degree.. In the STN method, the curve rises steeply in the vicinity of the threshold value, and it is possible to obtain a high contrast ratio even under a high duty ratio. However, because it utilizes the birefringence effect of the liquid crystal, the dependence of the display characteristics on the wavelength of light is higher than that of the TN display. Thereby, coloring of the display becomes much more severe.
Furthermore, in order to display a multicolor image, generally, a color filter layer is provided as described above. In this case, however, there are such problems that the manufacturing process therefor is complicated and the manufacturing cost increases.